Abstract B023: Enhancing the efficacy of oncolytic virus immunotherapy using eicosapentaenoic acid in preclinical cancer models

Abstract Introduction Despite significant advances in cancer immunotherapy, response rates remain limited and variable across patients and cancer types. Oncolytic viruses (OVs) are cancer immunotherapeutic agents, which kill cancer cells and promote an anti-tumor immune response. However, upregulation of immune evasion pathways, such as COX-2 mediated prostaglandin E2 (PGE2) signaling by cells in the tumor microenvironment (TME), including tumor associated macrophages (TAMs), can hinder their immunotherapeutic potential. This study investigated whether combining OVs with eicosapentaenoic acid (EPA), an omega-3 polyunsaturated fatty acid with anti-inflammatory properties, including inhibition of PGE2 production, could enhance OV anti-cancer activity. Methods Balb/c mice were injected with colorectal CT26 cells and treated with OV (reovirus), EPA, or a combination of both reovirus/EPA, and tumor growth was monitored. Upon sacrifice, immune cell infiltration within harvested tumors was assessed by immunohistochemistry (IHC). PGE2 and cytokine production was determined by ELISA while MTT assays were employed to measure cell growth inhibition, in vitro. Co-culture of cancer cells with human peripheral blood mononuclear cells (PBMCs) was used to generate tumor-associated macrophages (TAMs), which were then isolated by magnetic bead CD14+ cell separation Results Assessment of EPA and reovirus in vivo suggested that the combination treatment reduced tumor volume more than the single agent treatments and confirmed that EPA significantly reduced PGE2 production. The combination treatment strategy also significantly inhibited the production CXCL9 and reduced the percentage of arginase-1 positive cells, a marker of TAMs. In vitro, EPA supplementation did not alter abrogate reovirus direct oncolysis and furthermore potentially enhanced reovirus oncolysis of CT26 cells. Additionally, EPA supplementation hindered PGE2 production and significantly inhibited the in vitro generation of TAMs by 50-90%. Conclusion These results suggest that EPA could render the TME less immunosuppressive without compromising on the direct oncolytic effect of the virus, ultimately enhancing OV-based immunotherapy. Citation Format: Nametso Koobotse Khumo, Milene Volpato, Fiona Errington-Mais. Enhancing the efficacy of oncolytic virus immunotherapy using eicosapentaenoic acid in preclinical cancer models [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr B023.